The first line of code in your question appears to be the problem.
The get_the_terms() function expects the post (object or ID) as the first parameter. The second parameter should be the taxonomy name, not your custom post type.
Something like this should work for you:
$age_terms = get_the_terms( $post->ID, 'age' );
$lang_terms = get_the_terms( $post->ID, 'language' );
get_the_terms( int|WP_Post $post, string $taxonomy )
https://developer.wordpress.org/reference/functions/get_the_terms/